The present invention relates to an improved exhaust header for an internal combustion engine having an improved transition from primary pipes to a collector pipe for improving exhaust gas flow through the header.
A wide variety of header systems have been developed for exhausting combustion gases from the cylinders of internal combustion engines and directing the gases to an exhaust pipe in order to improve horsepower, vary the maximum torque band and improve fuel efficiency of the engine. Basically, a header includes a flange plate that bolts up to the engine""s exhaust ports, primary tubes that extend from holes in the flange plate at the exhaust port locations to a collector tube which collects the exhaust and directs it into the exhaust pipe having a muffler, catalytic converter, etc.
In the past, automobile manufacturers have provided cast iron header manifolds because they are easier to manufacture and emit less noise. However, these header systems provided less than ideal emission control and gas milage, so that tube-type headers are now provided on many new production cars. After market tube-type headers have long been offered both for improving street performance and for racing.
A variety of header designs have been developed. The most common is the 4-into-1 design in which four primary tubes from the flange to a collector or transition pipe where the total cross sectional area of the primary pipes is collected and reduced to the cross section of the exhaust pipe. In other designs, pairs of primary pipes are brought together, then the combined primaries are brought together in a collector. In pure race cars, the primary pipes from the flanges may be brought outside the vehicle independently, functioning as individual exhaust pipes. In other designs, primary pipes from opposite banks of a V-8 or V-6 engine may be brought together in a selected configuration.
Each of the header components has an effect on performance. For example, using a smaller primary tube diameter tends to lower the torque peak, which is advantageous in a street vehicle but not in a full race car. Longer primary tubes also increase low-end torque, as will a larger collector. Equal length primary pipes assure that each cylinder is scavenged equally. Uniform flow and avoidance of turbulence in the primary pipe, collector and exhaust system are important in reducing back pressure and maximizing both power and fuel efficiency.
The point where the primary pipes come together and enter the collector has been found to be a problem area in assuring smooth, non-turbulent exhaust gas flow through the collector. The cross sectional area of the combined primary pipe ends transitions through the collector to the (generally smaller) exhaust pipe cross section. The cross sectional area that is formed between the bundled primary pipe ends, approximately square with four primary pipes and approximately triangular with three primary pipes, is a major cause of turbulence.
Attempts have been made to smooth this transition by cutting back the adjacent surfaces of adjacent primary pipes, then welding them together to substantially eliminate the area between the pipe ends. This is difficult, expensive in design and manufacture, and with a number of complex welds may actually add to turbulence in this transition region.
Thus, there is a continuing need for improvements in header design to reduce or eliminate turbulence caused by the joining of adjacent primary pipes at the collector and transitioning to the exhaust pipe diameter.
The above-noted problems, and others, are overcome in accordance with this invention by an exhaust system for an internal combustion engine which basically includes a plurality of primary pipes, each extending from one of the cylinders to an end at a collector pipe, the ends of the pipes being in contact, substantially parallel and uniformly arranged about a central axis and lying substantially in a single plane, and a transition piece having a generally pyramidal shape with the base covering the areas between the adjacent primary pipe ends. Where four primary pipes are brought together, as would be the case with one bank of a V8 engine, the base of the pyramidal transition piece would be approximately square, while with the three primary pipes of one bank of a V-6 engine, the base would be approximately triangular. While straight-sided bases are generally effective, if desired for optimum performance, the base edges are preferably slightly concave to more precisely match the edges of the primary pipes. Also, the pyramid base will approximate a square or rectangle where four primary pipes are brought together, and will approximate a triangle where three primary pipes are brought together. Other configurations are used where other numbers of pipes are brought together, as is apparent to one skilled in the art.
The pyramidal transition pieces may have any suitable height. A height substantially equal to the length of one side of the base has been found to be effective and can easily be installed in the collector, even with a very compact system. In some cases optimum results are obtained where the height of the pyramid is sufficient to extend to the end of the collector, to provide the most uniform, smooth, transition from the greater total cross sectional area of the combined primary pipe ends to the lesser cross sectional area of the exhaust system. That change in area is known to promote exhaust system efficiency. Depending upon the collector pipe configuration, optimally the sides of the pyramidal transition piece may be slightly concave or convex (along a line taken through the center of a side surface from tip to base) to aid in providing precisely uniform flow cross sectional area reduction through the collector.
The transition pieces may be formed from any suitable material. In general, it is preferred that the material be the same as that of the primary pipes, typically 1010 or 1020 carbon steel, 308 or 221 stainless steel, etc. The transition pieces may be manufactured in any suitable manner. Typically, they may be cast from the appropriate metal or machined from solid stock to final dimensions. In a method that is preferred for low cost and ease of manufacture, two pieces, each making up two adjacent sides of the pyramid, are formed by stamping from heavy sheet metal. The pieces are then joined by welding. This requires only simple and inexpensive tooling, and permits easy production of pyramids with concave base edges and/or concave or convex sides if desired.